Injection molding systems that are configured to produce molded articles having multiple layers of varying thermoplastic compositions typically have a high capital cost relative to injection molding systems that are configured to produce molded articles of a homogenous thermoplastic composition. A molded article having multiple layers may be, for example, a multi-layer preform, of the type that is blow molded into a bottle. A typical multi-layer preform includes three layers, the inner and outer layer are made from a first thermoplastic composition, resin ‘A’, such as polyethylene terephthalate (PET), while an intermediate layer may be made from a second thermoplastic composition, resin ‘B’, such as ethylene vinyl alcohol copolymer resin (EVOH). The intermediate layer of ‘B’ resin is commonly referred to as a barrier, as it functions to prevent oxygen and other gases from permeating through the molded article which may otherwise adversely affect the quality of a product, such as a beverage, that is sealed in the bottle.
The high capital cost of multi-layer injection molding systems presents a capital burden for preform producers (converters), for example, when purchasing a multi-layer molding system without first securing firm contracts to supply the multi-layer preforms. Today, the long lead time required to procure a multi-material molding system make it difficult for converters to react quickly to business multi-layer preform supply opportunities from the relatively fast-paced preform consumer market without otherwise having idle multi-layer molding equipment at the ready. A field upgrade of a purpose built mono-layer molding system is not practical owing to the extent to which the molding structure of the system would need to be altered, not the least of which is a required machining of the stationary platen to incorporate a passageway to accommodate a second injection unit. The net effect of the foregoing is that preform converters have been reticent to go after multi-layer preform business.
U.S. Pat. No. 6,517,337 (Inventor: HEHL, Karl, Published: 11 Feb. 2003) describes an injection molding machine having a plurality of modular drive groups that provides possibilities for the customer to optimize the injection molding machine depending on the injection molded product.